SEGMENT REPORTING (Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 1,611,971	$ 1,611,827
Goodwill	478,728	465,154
Permits and other intangibles, net	477,639	498,721
Total assets	3,748,353	3,681,920
Technical Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	507,069	521,134
Goodwill	60,154	61,116
Permits and other intangibles, net	75,260	78,625
Total assets	848,578	862,957
Industrial and Field Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	264,662	245,143
Goodwill	112,365	107,968
Permits and other intangibles, net	17,139	17,817
Total assets	485,297	446,826
Safety-Kleen
Segment Reporting Information [Line Items]
Property, plant and equipment, net	585,493	584,647
Goodwill	306,209	296,070
Permits and other intangibles, net	377,458	391,390
Total assets	1,475,764	1,474,755
Oil, Gas and Lodging Services
Segment Reporting Information [Line Items]
Property, plant and equipment, net	177,106	182,038
Goodwill	0	0
Permits and other intangibles, net	7,782	10,889
Total assets	239,308	253,242
Corporate Items
Segment Reporting Information [Line Items]
Property, plant and equipment, net	77,641	78,865
Goodwill	0	0
Permits and other intangibles, net	0	0
Total assets	$ 699,406	$ 644,140